MILAN (AP) — Expo 2015 officials have heightened security measures surrounding the world's fair in Milan, which is expected to attract more than 20 million visitors over six months, following the terror attacks in Paris, the event's commissioner said Thursday.

The Expo grounds will be surrounded by a security fence, arriving visitors will be subject to controls similar to those at airports, including metal detectors, and more than 2,000 security cameras will be activated.

"The events in Paris made us focus even more attention on security, but this is work we started a long time ago," commissioner Giuseppe Sala said, noting that Expo has been working with Italy's Defense Ministry, secret services and local law enforcement for 18 months.

"I don't want to overdramatize the situation, but it is an event that could be subject to risks of that nature," he said.

With less than three months to the May 1 opening, Sala gave an overall positive report, noting that 8 million tickets had been sold, one-third of the 24 million projected, and 80 percent of the construction is finished.

Still, some countries, like late-comers Turkey and the Netherlands, are scrambling to finish in time. Latvia ran out of time and money, and pulled out this week, bringing to 53 the number of national pavilions, the largest of which belongs to Germany.

The site, about 15 kilometers (9 miles) northwest of Milan's center, is buzzing with some 3,500 workers completing the structures and grounds, including the planting of 20,000 trees, in time for the gala opening concert starring Andrea Bocelli.

Expo 2015, focusing on food and nutrition, has already weathered a corruption scandal that Sala acknowledged "was a terrible blow to our image." But he said it also led to even stricter contract protocols, including the appointment of an anti-corruption official.

The event, which cost the Italian government 1.3 billion euros ($1.5 billion), is expected to pump 10 billion euros into the economy before it closes on Oct. 31, Sala said. The 184 participating nations have invested another 1 billion euros.